| 1.0 | DEFINITION |
| A natural or constructed channel shaped or graded to required dimensions, and established in suitable vegetation for the safe disposal of runoff water. Grassed waterways may be used alone or in combination with diversion terraces and other structures to discharge surface runoff as part of an erosion control system . |
Grassed Waterways
2.0 GENERAL
| 2.1 | All grassed waterway design and construction shall be in accordance with Chapter 7 "Grassed Waterways and Outlets" of the USDA-SCS Engineering Field Manual for Conservation Practices and as specified in the following: |
| 2.2 | The NB Department of Environment Watercourse Alteration Regulations and Guidelines will apply to all projects including Regulation 90-80 and 90-120 under the Clean Water Act as revised in 1993. |
3.0 PLANNING AND DESIGN
| 3.1 | The minimum capacity shall safely convey the peak runoff expected from a 10 year frequency - 24 hour duration storm. If the waterway is used as an outlet for a companion conservation structure or within an urban / residential area the capacity will be increased to accommodate a higher design frequency (25 yr. - 24 hr. duration storm). |
| 3.2 | The design discharge used to determine the grassed waterway capacity shall be calculated using the USDA-SCS EFM2 method or the TR55 method. |
| 3.3 | Generally, the grassed waterway cross-section shall be parabolic to reduce meandering risk. Trapezoidal grassed waterway cross-sections are recommended for steeper slopes and for larger runoff discharge. See figure 1 - Typical waterway cross sections. |
| 3.4 | The minimum grassed waterway depth shall be 0.3 m (1.0 ft). The depth shall be increased as required to properly outlet diversion terraces and/or other structures that are designed to outlet into the waterway and to assure better row drainage. The recommended side slopes shall be 6:1 to 8:1 to improve waterway crossing and farmability. |
| 3.5 | The maximum grassed waterway width shall be less than 20 m (66 ft.) except where other suitable outlet locations or methods cannot be found. The minimum width shall be greater than 6 meters (20 ft) where crossing with farm equipment is required. |
| 3.6 | Where the design peak discharge of the grassed waterway is greater than 2.8 m3/s (100 cfs) and/or the design velocity is greater than the permissible velocity, the waterway shall be designed with a stone centre, non-degradable erosion control matting or in combination with other special conservation structures as required to safely discharge peak flow. |
| 3.7 | Subsurface drainage shall be installed as required to eliminate continuous or base flow in the waterway and provide proper conditions for vegetative growth. Drains shall be located on each side of the waterway and not installed within the centre two-third width of the waterway and shall. |
| 3.8 | Maximum permissible velocities shall be selected in accordance to values specified in table below, recommended in S.C.S., E.F.M.H. (Exhibit 7.3). |
| Cover | Slope Range (%) |
Permissible Velocity | |
| Erosion Resistant Soils m/s (ft/s) |
Easily Eroded Soils m/s (ft/s) |
||
Tall Fescue |
<5 5-10 over 10 |
2.13 (7) 1.82 (6) 1.52 (5) |
1.52 (5) 1.22 (4) 0.91 (3) |
| Grass Mixture Reed Canary grass |
<5 5-10 |
1.52 (5) 1.22 (4) |
1.22 (4) 0.91 (3) |
| Redtop Alfalfa Red Fescue |
<5 | 1.06 (3.5) | 0.76 (2.5) |
| 3.9 | For waterways with stone-lined centers, maximum permissible velocity in the above table may be increased by 2 ft/s or the maximum permissible velocity for erosion resistant soils maybe used. |
4.0 Construction and Maintenance
| 4.1 | All trees, brushes, stumps, obstructions and other objectionable material shall be removed from the side and disposed of in a manner consistent with environmental concerns and proper functioning of the waterway. |
| 4.2 | The waterway shall be excavated or shaped to the lines and grades as required to meet this standard and be free of bank projections or other irregularities which will impede normal flow. |
| 4.3 | Topsoil shall be removed from excavation areas and replaced during final grading as required to promote good vegetative growth. |
| 4.4 | Fill shall be compacted or field rocks used as required to prevent excessive/unequal settlement that would result in damage to the completed waterway. |
| 4.5 | Excessive subsoil removed during waterway construction shall be used for land forming, access road construction and/or stockpiled in an unused area outside of the waterway. |
| 4.6 | Grassed waterways designed and constructed as part of a system that diverts water runoff from its natural outlet shall require the written permission of affected downstream or adjacent landowners, or the Department of Transportation if road ditches are used. |
| 4.7 | A New Brunswick Watercourse Alteration Permit may be required for waterways constructed that outlets directly into a natural watercourse, such as a lake, river, or stream. |
| 4.8 | All construction operations shall be performed as required to reduce soil erosion, and shall be built in a period where seeding can take place prior to August 31 so adequate vegetative cover can be established to protect against fall and spring runoff. If constructed after August 31, waterway must be protected with appropriate erosion control matting to limit damage from runoff events until vegetative cover can be established in the following summer season. |
| 4.9 | Erosion control mats will be used in place of temporary ditches to encourage the proper establishment of vegetative cover in the waterway. The width of the mat installed shall be equal to the width of the waterway required to safely discharge a 5 year - 24 hour storm. |
| 4.10 | The owner of the grassed waterway shall be advised of other complementary soil conservation practices and of grassed waterway maintenance procedures. |
| 4.11 | Grassed waterways shall be properly limed, fertilized and seeded to recommended conservation grass mixture and maintained with a permanent weed-free sod cover. |
Fig. 1. Typical waterway cross sections.
The New Brunswick Department of Agriculture, Fisheries and Aquaculture reserves the right to revise the above standard at any time.